I don't think AT&T can detect if you are mining and I don't see any red flag if you mine while using this ISP but just in case you want to encrypt all of your mining activity then consider changing your DNS to a different DNS like Cloudflare to make sure you are submitting an encrypted data because if you didn't use other DNS your ISP can do deep packet inspection where they can know what site you are accessing to so changing DNS to cloudflare or google DNS will encrypt your data submitted to ISPs.
As an alternative to Cloudfare for a DNS resolver, would it work to implement a recursive DNS like Unbound[1]? This would increase greatly the privacy as the way that recursive DNS work is that they break down requests and go ask around DNS resolvers what address is associated with a certain IP in multiple stages. This would have a drawback of being slow the first few times but with time it would fetch data directly from the local cache. This is usually applicable in Pi-holes even, I just don't know if it would work correctly with traffic associated with miners.[1]https://github.com/NLnetLabs/unbound
